The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
(1) Field of the Invention
The present invention relates generally to underwater acoustic receiving sensors and, more specifically, to an underwater acoustic receiving sensor that measures the pressure, acoustic particle velocity, and the three gradients of acoustic particle velocity in such a manner as to improve the directivity of the underwater acoustic receiving sensor.
(2) Description of the Prior Art
Pressure sensors, or hydrophones, are commonly used to detect sound underwater. These sensors are omni-directional and can not distinguish the arrival direction of a sound source. Pressure sensors are often configured into an array of sensors, and the array then provides a means to estimate the source location. Better angular resolution is obtained by larger arrays of pressure sensors.
In the early 1990""s, new types of underwater acoustic receiving sensors were considered for sonar applications. Conventional underwater acoustic sensors measure acoustic pressure and are omni-directional. That means, the response of the traditional sensor is uniform in all directions. It is desired to have a non-uniform, or directional sensor, that can look in a given direction and reject noise arriving at other angular directions. Improvements have been made to acoustic receiving sensors. For example, the Conformal Acoustic Velocity System (CAVES) uses a sensor that measures a single component of acoustic particle velocity.
U.S. Pat. No. 6,370,084 discloses a device that measures pressure and three components of acoustic particle velocity at a collocated point; however, this device cannot measure pressure or gradients of acoustic particle velocity. It is desired that further improvements be provided for underwater acoustic sensors especially to improve their directivity.
Therefore, it is an object of the present invention to provide an underwater acoustic sensor having improved directivity in that it senses parameters, in the form of desired signals, received from selected directions and rejects noise arriving at other angular directions.
It is another object of the present invention to provide an underwater acoustic receiver sensor that measures seven quantities of an acoustic field at a collocated point. It is an additional object to measure acoustic pressure, three orthogonal components of acoustic particle acceleration, and three spatial gradients of the acceleration vector.
It is still another object of the present invention to provide an acoustic receiver having a directivity index of about 9.5 dB.
The underwater acoustic receiver sensor of the present invention measures pressure P0, three components of acoustic particle velocity (u,v,w), and three gradients of acoustic particle velocity             ∂      u              ∂      x        ,            ∂      v              ∂      y        ,            ∂      w              ∂      z      
all at a collocated point {overscore (r)}o in space. The underwater acoustic receiver sensor is capable of being mounted and comprises an enclosed housing having a center, x, y, and z axes, an interior of the housing filled with a polymer, and a pressure sensor rigidly attached at the center of the housing. The underwater acoustic receiver further comprises three pairs of collinear accelerometers a1-a2; a3-a4; and a5-a6 respectively arranged and attached along the x, y and z axes, respectively, within the housing and with each pair being oppositely positioned relative to the center of the enclosure and separated from each other by a predetermined distance l.